Evolving turbulence and magnetic fields in galaxy clusters

By K. Subramanian, A. Shukurov, Nils Erland L. Haugen. 2005

223 citations recorded by the source corpus.

We discuss, using simple analytical models and magnetohydrodynamic (MHD) simulations, the origin and parameters of turbulence and magnetic fields in galaxy clusters. Any pre-existing tangled magnetic field must decay in a few hundred million years by generating gas motions even if the electric conductivity of the intracluster gas is high. We argue that turbulent motions can be maintained in the intracluster gas and its dynamo action can prevent such a decay and amplify a random seed magnetic field by a net factor of typically 104 in 5 Gyr. Three physically distinct regimes can be identified in the evolution of turbulence and magnetic field in galaxy clusters. First, the fluctuation dynamo will produce microgauss (μG)-strong, random magnetic fields during the epoch of cluster formation and major mergers. At this stage pervasive turbulent flows with rms velocity of about 300 km s -1 can be maintained at scales of 100-200 kpc. The magnetic field is intermittent, has a smaller scale of 20-30 kpc and average strength of 2 μG. Secondly, turbulence will decay after the end of the major merger epoch; we discuss the dynamics of the decaying turbulence and the behaviour of magnetic field in it. Magnetic field and turbulent speed undergo a power-law decay, decreasing by a factor of 2 during this stage, whereas their scales increase by about the same factor. Thirdly, smaller-mass subclusters and cluster galaxies will produce turbulent wakes where magnetic fields will be generated as well. Although the wakes plausibly occupy only a small fraction of the cluster volume, we show that their area-covering factor can be close to unity, and thus they can produce some of the signatures of turbulence along virtually all lines of sight. The latter could potentially allow one to reconcile the possibility of turbulence with ordered filamentary gas structures, as in the Perseus cluster. The turbulent speeds and magnetic fields in the wakes are estimated to be of the order of 300 km s -1 and 2 μG, respectively, whereas the turbulent scales are of the order of 200 kpc for wakes behind subclusters of a mass 3 x 10 13 M ⊙ and about 10 kpc in the galactic wakes. Magnetic field in the wakes is intermittent and has the scale of about 30 and 1 kpc in the subcluster and galactic wakes, respectively. Random Faraday rotation measure is estimated to be typically 100-200 rad m -2 , in agreement with observations. We predict detectable polarization of synchrotron emission from cluster radio haloes at wavelengths 3-6 cm, if observed at sufficiently high resolution.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/71e3f6c1a9c50183f4b6e27ed8fae4c9fc550b1d

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Citations in the corpus

RESIDUAL GAS MOTIONS IN THE INTRACLUSTER MEDIUM AND BIAS IN HYDROSTATIC MEASUREMENTS OF MASS PROFILES OF CLUSTERS (2009, background): “…effects of AGN feedback, and cosmic rays injection and evolution should provide some guidance as to the radial dependence of contributions from magnetic fields and cosmic rays, as non-thermal sources of pressure support (e.g., Subramanian et al. 2006; Pfrommer et al. 2007; Sijacki et al. 2008).”
Massive and refined - II. The statistical properties of turbulent motions in massive galaxy clusters with high spatial resolution (2010, background): “…of AGN that are found in the central cluster galaxies may excite turbulence in the cores of the hosting clusters (e.g. Fabian et al. 2003; Rebusco et al.2005; Scannapieco & Br¨uggen 2008), as well as galaxies that cross the cluster atmosphere (e.g. Deiss et al 1996; Subramanian et al. 2006).”
Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMR (2009, background): “From the theoretical point of view, turbulenc can be injected in the IGM by several mechanisms: plasma instabilities, cluster mergers and shock waves, wakes of galaxies moving into the IGM, outflows from AGNs hosted in the center of galaxy clusters and galactic winds.”
Acceleration of primary and secondary particles in galaxy clusters by compressible MHD turbulence: from radio haloes to gamma-rays (2010, background): “Theoretically we expect that magnetic field can be amplified by turbulence in the IGM (e.g. Subramanian et al 2006), although as a necessary simplification we do not include that amplification process in our calculations.”
Small-scale dynamo action during the formation of the first stars and galaxies - I. The ideal MHD limit (2010, background): “As shown e.g. by Subramanian et al. (2006), the power-law behaviour of the total energy results from an exponential decay of the magnetic field on a given scale, which happens on the eddy-timescale.”
Shocking results without shocks: Subsonic turbulence in smoothed particle hydrodynamics and moving-mesh simulations (2011, background): “Besides this direct observational evidence, there are also strong analytic arguments that suggest that hierarchical mergers should be able to generate and sustain subsonic turbulence in galaxy clusters (Subramanian et al. 2006).”
Astrophysical magnetic fields and nonlinear dynamo theory (2004, methodology): “200 rad m−2 as observed, when scaled to cluster parameters [558].”
Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration (2007, background): “…in the physics of the ICM as it is necessary to understand the amplification of magnetic fields in clusters (Dolag et al. 2002; Schekochihin et al. 2005; Subramanian et al. 2006), an issue closely related to the non–thermal emission from clusters but that we will not address in this paper.”
The Interplay of Magnetically Dominated Turbulence and Magnetic Reconnection in Producing Nonthermal Particles (2019, background): “…Brandenburg & Subramanian 2005), jets from active galactic nuclei (Marscher et al. 2008; MacDonald & Marscher 2018), radio lobes (Vogt & Enßlin 2005; O’Sullivan et al. 2009), gamma-ray bursts (Piran 2004; Kumar & Narayan 2009), and galaxy clusters (Zweibel & Heiles 1997; Subramanian et al. 2006).”
Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating (2010, background): “…& Norman (1998); Roettiger et al. (1999b); Inogamov & Sunyaev (2003); Schuecker et al. (2004); Faltenbacher et al. (2005); Dolag et al. (2005); Subramanian et al. (2006); Schekochihin & Cowley (2006); Vazza et al. (2006); Iapichino et al. (2008); Iapichino & Niemeyer (2008); Maier et al.…”
ASTROPHYSICAL GYROKINETICS: KINETIC AND FLUID TURBULENT CASCADES IN MAGNETIZED WEAKLY COLLISIONAL PLASMAS (2007, background): “…supernova explosions in the ISM (e.g., Norman & Ferrara 1996; Ferrière 2001); the magnetorotational instability in accretion disks (Balbus & Hawley 1998); merger events, galaxy wakes and active galactic nuclei in galaxy clusters (e.g., Subramanian et al. 2006; Enßlin & Vogt 2006; Chandran 2005a).”